Xbee Series 1 and API mode - What PINS do I need??

Hi,

I have two Xbee series 1 modules. On the transmitter module I soldered connections to Vcc, Gnd, Data In. On the receiver module I soldered connections to Vcc, Gnd, Data Out.

I connected these to two arduino boards and was able to send data from Tx to Rx using AT mode.

Now I want to try sending data packets from the Tx to Rx but I want to know do I need to use any of the other pins on the Xbee modules to allow me to do this??? I know in API mode acknowledgments can be sent back from the Rx so do I need to solder connections to the Data Out pin on the transmitter and Data In pin on the receiver to allow this??

If I dont want to use acknowledgements but want to use API mode can I use the current connections I have?

Thanks.